The Core Facility for Aged Rodents (CFAR) provides animals and advice for research scientists who wish to use animal models to study the biology of aging, the relationship between aging and disease, or therapeutic approaches that could lead to the development of human intervention trials relevant to the independence and health care of the elderly. CFAR is directed by Dr. Richard A. Miller, Professor of Pathology and the Associate Director for Research of the Geriatrics Center. Veterinary consultation is provided by Dr. Robert Dysko, DVM, Assistant Professor of Laboratory Animal Medicine. Aged and control rats and mice are purchased from the NIA Contract Colonies and supplied to recipients of Pepper Center Pilot/Feasibility Grants, to junior faculty scientists who wish to acquire pilot data towards the preparation of an application for OAIC or extramural support, and to established scientists who wish to begin study of a problem in geriatrics or gerontology for which they do yet have external support. This facilitated access to old rodents serves to attract developing and established scientists to experimental geriatrics and to facilitate their initial forays in this field, while at the same time ensuring that they obtain advice (from the Core Director) on matters of choice of strain and species, appropriate selection of age groups, and possible influence of overt or latent diseases. Core resources are also devoted to the development of novel animal models that present unique advantages for studies of aging and geriatric diseases. Four such models are currently under development: (a) "HET" mice, bred by a four-way cross from inbred grandparents, to provide a degree of reproducible genetic and phenotypic heterogeneity that more closely resembles the variation present in aging human populations; (b) the WI/Hicks/Car rat whose lack of adult growth makes it particularly suited for studies of cross-age transplantation (e.g. of muscle and nerve grafts); (c) the mdx/mdx mouse that develops a mild form of muscular dystrophy in early adult life and that may provide a useful model of late life myopenia; and (d) the T(X;16)16H x SPE (Mus spretus) F1 hybrid mouse, a cross-species hybrid useful for investigations of X chromosome gene reactivation in aging. CFAR thus provides Pepper Center and other U/M researchers with consultation on experimental design, facilitated access to aged rats and mice, and assistance in producing and characterizing new rodent models that are particularly useful for studies of aging and not available elsewhere.